Workshop on Low Corrosion Rates ASTM Committee G-1 May 18, 2005, Reno, NV

Workshop Chairs Sheldon W. Dean Neal S. Berke Sean Brossia

Traditional Concepts Negligible corrosion rate: <1 mpy Primary concern: loss of strength Service Life: <10 to 50 years Low corrosion rate problems occur when these concepts do not apply

Low Corrosion Rate Cases Nuclear waste storage: 100K years Medical implants: reaction to c.p.’s Semiconductor manufacturing: c.p.’s Sterile water: rouging

Workshop Objectives Examine actual examples of LCR’s Learn state of art Can standards development assist in coping with LCR problems?

Standards Development: ASTM G-1 Scope Promotion of knowledge Stimulation of research Collection of engineering data Development of standards: –Corrosion –Methods for corrosion protection

Types of G-1 Stds. Test methods Practices Guides Classifications Specifications Terminology

Workshop Program Introduction: S.W.Dean Lab Corrosion Testing of Medical Implants- R. Corbett Rouging- a Discoloration of Stainless Steel- R. Corbett Rouging: Issues Facing the Pharmaceutical & Biotech Industries- P. Banes

Rouging -Terminology Terminology – G01.02 Meeting Development of colored, usually red or brown, layer on stainless steel in pure or sterile water Not usually associated with localized corrosion Not well understood

Rouging - Conditions Major concern for water for injection, WFI Also seen in other sterile water systems Water usually >60°C Water is air saturated Low impurity levels, 10 –100 ppm Cl Long residence times, days or weeks

Rouging Concerns Cosmetic – Systems look dirty, unacceptable for medical purposes Contamination of product with corrosion products Future regulation from FDA?

Rouging Mechanisms Deposition of film from colloidal solution Precipitation of film from supersaturated solution Growth of passive film

Colloidal Deposition Passive film dissolves in water releasing ferric ions Ferric ions precipitate in solution to form colloidal particles Particles adhere to stainless steel surface Mechanism requires particles to be less soluble than passive film

Precipitation Passive film dissolves releasing ferric ions Ferric ions precipitate on stainless surface Film forms and grows Problem: How can passive film dissolve and precipitate at the same time?

Passive Film Dissolution Passive film is amorphous, contains OH – Fe(OH) 3 is much more soluble than ferric oxides Fe +3 from Fe(OH) 3 can precipitate FeOOH or Fe 2 O 3

Growth of Passive film Normal passive film very thin: 10 – 100nm Oxidizing conditions cause passive film to thicken at a decreasing rate When film exceeds 200 nm it becomes visible

Important Questions Potential of stainless steel during rouging? Nature of rouge, crystalline or amorphous? Type of crystal? Particle size and degree of organization of rouge? Chemical composition of rouge?

MTI Program Purpose: to gain fundamental understanding of mechanism Project development team formed Champion: M. Renner, Bayer Staff: F. G. Hodge Pourbaix (Potential- pH) diagrams calculated

Thank You!